Known colloquially as the may bush, this frost-tolerant spring-flowering shrub can grow to 2 m tall. In September it is smothered in frothy pure white fountains of bloom, each flower like a posy of single or double tiny blooms. The double-flowered form, called 'Flore Pleno', is most commonly seen, but the single form is also charming, and its blooms fall cleanly from the shrub when spent, whereas in the double-flowered form, these may hang on the shrub after they have aged and turned brown.
Spiraea looks at its best when its long branches are allowed to arch over, so sufficient space must be allowed for it to achieve this natural form. A few whole branches can be pruned right back to the base of the shrub each year immediately after flowering to allow this shape to be maintained. It looks particularly fetching when it weeps over a low front fence or retaining wall, or grown as an informal hedge. Some people like to clip it into a ball shape or a formal hedge. Whilst once I felt this treatment destroys its appeal, in recent times I have clipped my specimen into a dome, because it was being swamped by other plants in its border, and its loose shape was a liability rather than a feature.
Like many of the shrubs which appear in our spring gardens, the may bush originates in China. It will flower best in sunny spot in moist, well-drained soil, but it is an adaptable plant and copes well with quite ordinary garden positions, and dry times, once established. It was traditionally grown with evergreen azaleas in Sydney gardens; I like it as part of a scheme with other pure white flowers of September such Primula malacoides and a big white-flowered Abutilon, along with the pristine emerging foliage of white-striped grass Miscanthus sinensis 'Variegatus'.
Big branches of may bush cut when in bloom can make a spectacular flower arrangement in a big vase! And the flowers cut into tiny florets make an eco-alternative to confetti for weddings, as I discovered in September 2021!
Postscipt: Eventually, I took my old may bush out as it took up so much space. I still miss the beauty of its flowers each spring and the memory of my daughter's 'micro-wedding' during COVID that they evoked.